Three main results of our work are: 1. The pigment epithelium in frog retina generates a current that is monotonically related to the amount of free opsin in the rods and can be used as a measure of dark adaptation of the rods. This selfsame current is in turn related monotonically to the running maximum interpulse intervals on the dimming detectors (type 4) during dark adaptation of the rods. The pigment eipthelium removed, the dimming detectors do not show activity related to dark adaptation but function as simple "off" fibers. 2. A theory of color vision has been elaborated that takes as its generative function the cone curves for instantaneous threshold of split field at levels different from the adaptation level, as first done by Craik. The resultant space of "perceptual color" is not affine transformation of chromaticity space (the space of color matches). 3. The distribution of dehydrogenases across the retina suggests that metabolic cycles are shared between layers, rather than being complete in each layer. This result in turn makes the superficial retinal circulation more understandable, since now the sharing does not deprive the deepest layers when the more superficial layers are active.